Elevator-based tool loading and buffering system

ABSTRACT

An exemplary embodiment a substrate transport system is provided. The system has a guideway and at least one transport vehicle. The transport vehicle is adapted for holding at least one substrate and capable of being supported from and moving along the guideway. The guideway comprises at least one travel lane for the vehicle and at least one access lane offset from the travel lane allowing the vehicle selectable access on and off the travel lane.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. patent application Ser. No. 11/211,236, filed Aug. 24, 2005 and claims the benefit of U.S. Provisional Application No. 60/604,406 filed Aug. 24, 2004 which are incorporated by reference herein in its entirety.

BACKGROUND

1. Field

A system and method are disclosed for transporting reduced-capacity wafer carriers within a semiconductor fabrication facility.

2. Brief Description of Related Developments

There is a desire in the semiconductor industry to reduce wafer cycle time through the fab and reduce the amount of work in progress as well as to improve wafer safety. Studies have shown that by moving to a single wafer carrier, wafer cycle time and WIP (wafers in process) is significantly reduced. In addition for the next generation wafer size (450 mm) the ITRS roadmap calls for single substrate carriers. Benefits of using single wafer or reduced capacity carriers include WIP reduction, process changeover time reduction and product ramp time improvement. Problems arise where conventional single substrate carriers are employed relative to the ability of both the process tool and material transport system to effectively maintain the higher pace of the factory due to the larger number of carrier transport moves as compared to 13 or 25 wafer carriers. One example of such a problem includes where there is only one slot. It is desired that the robot in the process tool have the capability to quickly swap (fast swap) the wafer in the carrier so the carrier may be able to be replaced with another carrier that has an unprocessed wafer to keep the tool busy. Many such tools do not have the ability to fast swap, as in the case of a conventional single blade three axis robot. Another example of such a problem includes where there is only one slot. It is desired that the material transport system transporting carrier to tools in the IC FAB have the capability to supply carriers, at a high rate and quickly swap the carriers at the process tools load port(s) so that one carrier at the tool may be able to be replaced with another carrier that has an unprocessed wafer to keep the tool busy. Many such material transport systems do not have the ability to supply carriers at a high rate or with the capability to fast swap, as in the case of a conventional (overhead transport) OHT based material transport systems as implemented in conventional 300 mm fabs. Conventional material transport systems are highly rigid in the transport or movement scheme of the carriers transported thereby, and do not offer sufficient transport flexibility desired with carriers having reduced workpiece capacity (e.g. less than conventional 13 or 25 workpiece pods). For example, conventional transport systems, whether a continuous moving support based (e.g. conveyor belt or roller system) or a vehicle based e.g. discrete vehicles traversing on rails, tracks), employ substantially linear travel pathways with intersections or junctions for transport switching between different pathways. The travel pathways are generally unidirectional each allowing vehicles, or otherwise transported materials (e.g. workpiece carriers) moving on the pathway to move serially in sequence along the given direction of the pathway. Thus vehicles or transport material move along the pathway in progression with no availability of passing. Opposing pathways are provided for bidirectional movement (e.g. advance pathway and return pathway). In addition to service pathways, which communicate with the FAB tools/tool stations (i.e. the service pathway has locations where the transport material or vehicles traversing along the pathway may be stopped for interface to FAB tools), the conventional transport systems may have dedicated bypass or high speed (relative to the available transport speed on the service pathway that is limited by the inability to overtake stopped transport) pathways between pathway junctions. Nevertheless, the high speed pathways do not enable transport on a service pathway to pass stopped or slowed transport on the service pathway. Moreover transport along a high speed pathway of a conventional transport system remains linear (in serial sequence) still without ability to pass. Thus, if a transport stops on the high-speed pathway for whatever reason (e.g. breakdown) the other transport on the pathway cannot go around, pass the stopped transport, and continue on the pathway. As may be realized, the rigidity of the transport scheme of conventional material transport systems impairs the ability in directing workpieces to the full advantage of FAB tool availability with a commensurate degradation in the achievable FAB throughput. The exemplary embodiments overcome the problems of conventional systems as will be described in greater detail below.

Examples of transport systems, carriers and openers may be found in U.S. Pat. No. 6,047,812; RE38,221 E; U.S. Pat. Nos. 6,461,094; 6,520,338; 6,726,429; 5,980,183; 6,265,851 United States Patent Publications 2004/0062633, 2004/0081546, 2004/0081545; 2004/0076496 and pending Brooks Automation application Ser. No. 10/682,808 all of which are incorporated by reference herein in their entirety.

SUMMARY OF THE EXEMPLARY EMBODIMENTS

In accordance with an exemplary embodiment a substrate transport system is provided. The system has a guideway and at least one transport vehicle. The transport vehicle is adapted for holding at least one substrate and capable of being supported from and moving along the guideway. The guideway comprises at least one travel lane for the vehicle and at least one access lane offset from the travel lane allowing the vehicle selectable access on and off the travel lane.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic top plan view of a substrate processing system incorporating features in accordance with an exemplary embodiment;

FIGS. 1A-1B are respectively another schematic top plan view and a schematic elevation view of the substrate processing system in FIG. 1;

FIG. 2 is a schematic plan view of a substrate processing system in accordance with another exemplary embodiment;

FIG. 3A is a schematic to plan view of a transport system guideway and transport vehicle of the substrate processing system in accordance with another exemplary embodiment;

FIG. 3B is a schematic top plan view of a guide portion of the transport system guideway in accordance with another exemplary embodiment;

FIG. 3C is a schematic top plan view of the transport system guideway and a portion of the transport vehicle in accordance with another exemplary embodiment;

FIGS. 4A-4B are respectively a schematic plan view and elevation view of a transport system guideway and transport vehicle in accordance with another exemplary embodiment;

FIGS. 5A-5B are respectively a schematic plan view and elevation view of a transport system guideway and transport vehicle in accordance with another exemplary embodiment;

FIG. 6 is a schematic elevation view of the transport system guideway and transport vehicles in accordance with another exemplary embodiment, the vehicles being shown in different positions on the guideway;

FIG. 7 is a schematic top plan view of the transport system guideway, transport vehicle and carriers in accordance with another exemplary embodiment;

FIGS. 8A-8C are elevation views of the transport system guideways, transport vehicles and processing apparatus in accordance with still another embodiment; FIGS. 8A-8B are end elevations and FIG. 8C is a side elevation, and each respectively show the transport vehicles in different positions;

FIGS. 9A-9E are schematic elevation views showing a transport vehicle in accordance with respectively different exemplary embodiments;

FIG. 10 is a schematic elevation view of the transport vehicle, carriers C on the vehicle, in accordance with another exemplary embodiment, buffer and load port stations of a processing tool; FIGS. 11 and 12A-12C are respectively an elevation view of a portion of the transport vehicle and a carrier C registered to the vehicle, perspective views of carriers each having registration features in accordance with different exemplary embodiments, and FIG. 12D is a schematic cross-sectional view of a chuck in accordance with the prior art;

FIG. 13 is a schematic elevation view of the transport system guideways, transport vehicle and a substrate processing station in accordance with another exemplary embodiment;

FIGS. 14A-14D are schematic plan views showing the motive system of the transport vehicle in accordance with different respective exemplary embodiments, and FIG. 14E is a schematic elevation view of the transport vehicle;

FIG. 15 is a schematic plan of the transport vehicle control system;

FIGS. 16A-16C are side elevation views of a portion of transport system guideways and transport vehicle respectively showing the transport vehicle in three different positions, and FIGS. 17A-17C are end elevation views corresponding to the side views in FIGS. 16A-16C;

FIG. 18 is a schematic side elevation view of transport system guideways and transport vehicle in accordance with another exemplary embodiment, the vehicle being shown in different positions; and FIGS. 18A-18B are cross-section views respectively taken along view lines A-A and B-B in FIG. 18; and

FIGS. 19A-19C are end elevation views of transport vehicle of the transport system in accordance with another exemplary embodiment, respectively showing the vehicle in different configurations.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Referring to FIG. 1, a schematic plan view of a substrate processing system incorporating features of the disclosed embodiments, located in a fabrication facility or FAB is illustrated. Although the embodiments disclosed will be described with reference to the embodiments shown in the drawings, it should be understood that the embodiments disclosed can be embodied in many alternate forms of embodiments. In addition, any suitable size, shape or type of elements or materials could be used.

The substrate processing system 10 in the exemplary embodiment shown in FIG. 1 is representative of any suitable processing system and generally comprises processing tools S (two are shown for example purposes) transport system 10 and system controller 300. The transport system 10 generally comprises a guideway and transport vehicles 14. In the exemplary embodiment shown, the guideway 12 may be a passive guideway providing transport lanes TL, AL for the transport vehicles 14. There is at least one travel lane TL and at least one access lane AL. The transport vehicles 14 may be capable of autonomous travel (as will be described below) on paths along the lanes TL/AL formed by the guideway 12. The transport vehicles 14 (two vehicles 14 as well as a recovery vehicle 14R, described later are shown in FIG. 1 for example purposes) are each capable of holding and transporting one or more substrate carriers C along the guideway to the desired processing tools or processing tool stations S connected by the guideway 12. Vehicles 14 may be seated over or suspended from the guideway 12. Vehicles may access the process tools S from the access lane AL. The travel lane TL is available to vehicles for bypassing stopped or slowed vehicles in the access lane AL. The vehicles may move freely between travel and access lanes and vice versa.

FIG. 1 illustrates merely a representative portion of the guideway 12, and the guideway may extend as desired, and have any suitable shape so that the transport paths provided thereby for the vehicles 14 allow the vehicles access to any desired number of tool stations S in any desired locations for transfer of carrier C between tool station and vehicle. The substrate processing tool at a given tool station S may be of any desired type such as a fabrication tool (e.g. The GX series tool from Brooks Automation Inc.), a stocker or sorter. The tool may have a casing or enclosure defining an interior space into which substrates (independent of carriers) or the carriers themselves are loaded/unloaded. A suitable example of a tool is disclosed in U.S. patent application titled “ELEVATOR-BASED TOOL LOADING AND BUFFERING SYSTEM”, attorney docket No. 390P011937-US(PAR), filed Aug. 23, 2005, incorporated by reference herein in its entirety. The carrier C may be any suitable type of carrier capable of holding workpieces such as substrates (e.g. 200, 300, 450 mm (or any other diameter/size semiconductor wafer, rectile or flat panel for flat panel displays). The carrier may have a casing capable of holding the substrates in a controlled atmosphere. The carrier C may be a reduced capacity carrier. Reduced capacity carriers may have a capacity of fewer than the conventional 13 or 25 wafers and may be constructed in a manner similar to the FOUP defined in SEMI 347, but characterized by reduced height and weight. A suitable example of a substrate carrier is disclosed in U.S. patent application titled “REDUCED CAPACITY CARRIER AND METHOD OF USE”, attorney docket No. 390P011935-US(PAR), filed Aug. 19, 2005, which is incorporated by reference herein in its entirety. The carrier may be front (side) opening or bottom opening. In alternate embodiments, the carriers may be any other desired type of carrier as the features of the exemplary embodiments disclosed are equally applicable to transport system for any kind of workpiece carrier. The guideway 12 may be formed from any suitable structure and is shaped (i.e. has suitable rides surfaces 12S for vehicles 14 to ride on and adequate width) in this embodiment to provide both, what shall be referred to as, a travel lane TL and an access lane AL (as will be further described). The guideway 12 may be located at any desired height in the FAB. For example, the guideway may be at floor level of the FAB (the edges or borders of the guideway shown in FIG. 1 in such a case may not substantively exist (i.e. may not be formed by structure) but rather are virtually defined by the travel paths of the vehicles traversing along the lanes TL, AL (i.e. space envelope of the vehicles moving on the lanes). The guideway 12 may also be elevated, for example suspended from above or supported from below at a distance above the floor. As seen in FIG. 1, the guideway 12 may be positioned along a desired interface side of the tool stations S (or alternatively the tool stations may be located along the side of the guideway). The guideway 12 has interface stations I, corresponding to the locations of the tool stations S, where the vehicle may be stopped for transfer of carriers C between vehicle 14 and tool station S. The tool stations are located in the access lane AL. In this embodiment the transfer of carriers between tool station and vehicle at an interface station I is in a lateral direction to the guideway 12 (see also FIG. 1B which is an end elevation of interface station I). Referring also to FIG. 2, there is shown a schematic plan view of a transport system guideway 10′ in accordance with another exemplary embodiment. In the embodiment shown in FIG. 2, the guideway 12′, which is generally similar to guideway 12 in the embodiment shown in FIG. 1, is located overhead the tool station S. In this exemplary embodiment, the interface station I on the guideway (which as seen in FIG. 2 is in the access lane AL′) may be defined by an opening O in the guideway structure. The opening is sized to allow carrier transfer to/from the vehicle 14′ in a direction normal (i.e. down) to the guideway. Such a pass-through O enables placement of the access lane directly over the loadports, thereby reducing the aisle width used to accommodate elevated guideways. The active element transitioning carriers to and from vehicles may reside on the vehicle or the mating equipment, or be grounded at the point of transfer. In alternate embodiments, the transfer direction from an overhead guideway may be a combination of lateral (outward) and down, and the guideway may not have a through hole for carrier passage during transfer (e.g. carrier transfer would be over the side). The vehicle is configured to be able to traverse the opening. As seen in FIGS. 1-2, in this embodiment the travel and access lanes TL, AL of the guideway are substantially co-planar and communicate with each other in a substantially unrestricted manner along the length of the guideway 12. As may be realized the designation of the lanes as travel or access lanes is discretionary (the lane designation shown in the figures is for example purposes) as whether a lane serves as access or travel lane (or both) is related to the arrangement of the interface stations I (i.e. locations of tool stations). Moreover, the designation of access travel lane may be transient. For example, tool stations S, and hence interface stations I may be located in both lanes of a guideway 12″ (see FIG. 1A). In the exemplary embodiment shown in FIG. 1A, a vehicle 14″ is stopped at an interface station I″, in what may be referred to, at least while the vehicle 14″ is stopped, as access lane AL″. The adjoining lane serves as a travel lane for passing vehicles 14A″, and hence may be referred to as a travel lane. As seen in FIG. 1A, an interface station IA″ may be located in that lane as well. However, the interface station IA″ is unoccupied by a vehicle and hence the lane may operate as a travel lane. When locations of occupied interface stations I″, IA″ become reversed, then the designations of travel and access lanes respectively reverse. In alternate embodiments, the interface stations I″, IA″ in the different lanes may be sufficiently distanced along the guideway so that a vehicle may weave around occupied interface stations in opposite lanes. In that case, each lane would have an access lane portion, generally commensurate with the interface station, and a travel lane portion located substantially across from the interface station in the opposite lane. The transport vehicle may transition/cross freely between lanes to continue unimpeded travel along the travel lane(s).

The guideway 12 may have a guidance system 16 connected to controller 300 for enabling vehicle guidance on transport paths T1, ALE, A1 along the travel lanes TL, AL of the guideway 12 (see FIG. 1). The travel paths on the travel lanes illustrated in FIG. 1 are merely representative, and the vehicles may move along any desired transport path. In the exemplary embodiment shown in FIG. 1, the guidance system 16 may include positioning devices 16A allowing for position determination of the vehicles 14 moving on the guideway lanes. The positioning devices may be of any suitable type such as continuous or distributed devices 16T, such as optical, magnetic, bar-code, fiducial strips, that extend along the guideway and across (strip 16A) the guideway. The distributed devices 16P, 16A may be read or otherwise interrogated by a suitable reading device on the vehicle 14 to allow controller 30 to establish one or both of longitudinal and/or lateral position of the vehicle on the travel, access lanes TL AL of the guideway as well as kinematic state of the vehicle. Alternatively, the devices LGP may sense, interrogate a sensory item on the vehicle to identify position/kinematics. The positioning devices 16P may also include, alone or in combination with distributed devices 16T, 16A, discrete positioning devices (e.g. laser ranging device, ultrasonic ranging device, or internal positioning system akin to internal GPS, or internal reverse GPS) able to sense the position of the moving vehicle. The controller 300 may combine information from the guidance system 16 with position feed back information from the vehicle as will be described further below, to establish and maintain the transport path(s) of the vehicle along and between the travel and access lanes TL, AL of the guideway.

The guideway surface 12S may also be formed to define vehicle physical guides S16T, S16A that may, if desired form part of guiding system 16. In alternate embodiments the guideway may be provided with a guidance system with no physical guides. In other alternate embodiments, the guidance system may not have remote sensors. The guideway surface may include or have grooves, rails, tracks or any other suitable structure forming structural or mechanical guide surfaces to cooperate with mechanical guidance features on the vehicles 14. The guideway surface 12S may also include electrical lines, such as a printed strip, or conductor providing electronic guidance for the vehicles (e.g. electrical lines sending a suitable electromagnetic signal that is detected by suitable guidance system on the vehicles 14). The guideway 12 also has power system 18 incorporated therein for powering the vehicles. The power system 18 may include a continuous power system 18P, 18T, 18A, such as conductors or a printed strip, disposed on the guideway structure and capable of supplying power (e.g. AC current) to the vehicle 14 as it travels. Although in this embodiment the continuous power lines 18P, 18T, 18A are shown separate from the guidance system 16, 16T, 16A, in alternate embodiments the power lines may be incorporated into guidance means (e.g. the power lines may be used to provide electronic/electrical guidance for the vehicle). The power system 18 may also include for example discrete power supply stations 18PD, where the vehicles 14 may be charged. The power supply stations 18PD (one is shown only for example purposes) may be located as desired, such as at locations where the vehicles 14 are expected to stop, such as for example an interface station I where transfer of carriers may occur, as illustrated in FIG. 13. In embodiments where present, the guide surface S16T, S16A of the guidance system 16, may define the paths T1, AL1, ALi on lanes TL, AL on which the vehicles 14 may travel (though it may also be possible for the vehicles 14 to travel on the guideway 12 off the paths on lanes TL, AL). Though only one lane TL, and accompanying access lane AL is shown for example in FIG. 1, the guideway 12 may encompass any desired number of travel and access lanes and any desired number of travel and access paths on the corresponding travel and access lines similar to lanes TL and AL. The other lanes may be parallel to lanes TL, AL, or may be disposed in any other orientation. The travel paths in travel lanes TL may include furcations 20 (structural in the case of physical guides, or virtual where no physical guides are used) where paths onto the access lane AL, AL1-Ali merge/diverge from the travel lanes TL paths. As seen in FIG. 1A, the access paths AL1 (though only two are shown in FIG. 1A, the access lane AL of guideway 12 may have any desired number of access paths similar to path AL1, Ali disposed serially along path TL and/or in parallel at each furcation 20) connect the travel path TLI to interface I where carrier transfer may occur between the vehicles 14 and an intermediate transport (not shown) servicing corresponding stations S. The access paths on the access lane AL may be defined by guidance system 16, and again may be virtual in the case where no physical guides exist, or may be structural defined by portions S16A (and power supply means 18PA), and may in this embodiment have two entry/exit portions at opposite ends of the access path as shown in FIG. 1. As seen in FIGS. 1-2, the access path AL1-Ali provides an access way as well as a side path or siding to travel path TL1 (the vehicles 14 may be moved onto the access lane AL without having to transfer containers from or onto the vehicle at the interface) station. Thus, vehicles may be paused if desired on the access lane. Also, inoperable vehicles may be moved, for example using another vehicle, or manually onto the access lane. Further, the access lane may have as a buffer for queuing vehicle.

As noted before, at least one autonomous wheeled vehicle 14 is employed on the passive guideway 12. The vehicle 14 may be propelled, for example, by an on-board electric motor 14M through a friction drive. Energy for traction and other uses can be stored on the vehicle in ultra-capacitors and/or batteries, or as mechanical energy (e.g., with a flywheel). Recharging the stored energy can be accomplished at discrete locations 18PD or continuously along the guideway 18P, 18PT, 18PA through contacting or non-contacting means.

In the exemplary embodiment, ultra-capacitors 14C may serve as the primary energy storage devices due to their potential for rapid recharge. While charging, energy is transferred from guideway 12 to vehicle 14 across mating contacts (not shown) in the form of alternating current. Transferring AC is desired to DC because it is inherently self-quenching relative to arcing, a common failure mode in DC contact charging. Additionally, there may be significant material cost and cost-of-ownership savings associated with the elimination of grounded DC supplies and improved distribution efficiency. In alternate embodiments however, DC current may be used.

As noted before, the exemplary embodiment, position feedback for vehicle trajectory control may be achieved by continuous odometry, using encoders and/or resolvers at the vehicle wheels, periodically updated using external references (e.g., optical or magnetic encoding, bar-codes, fiducials, laser- or ultrasonic-ranging, etc.) of the guideway guidance system 16. FIG. 15 is a schematic plan view of a vehicle 14 being guided between two positions (POS1, POS2). In this embodiment, POS2 represents the position of the vehicle at an exemplary interface station I of the guideway and may be a final position. In FIG. 15, the initial position of the vehicle identified as POS1 may be located anywhere on the guideway. For example, POS1 may be on the access lane, or on the travel lane. The path PT between the initial and final positions of the vehicle is representative in this embodiment, and any suitable path may be selected by the controller 300. The controller may identify initial position POS1 of vehicle 14 from the vehicle encoder information, or guidance system 16 or both. The controller may continuously monitor the vehicle position, or may employ selective monitoring for example, arrival of the vehicle at position POS1 (identified to the controller by the vehicle odometry information, or sensed by guidance system 16) may cause the controller to identify the vehicle location. The controller may be suitably programmed to identify the destination of the vehicle (e.g. POS 2 or some other position past POS 2 and with respect to which POS 2 is a waypoint) and to send steering commands to the vehicle causing the vehicle to move along path PT to POS 2. Position feedback when the vehicle is traversing along path PT may be provided as noted before.

FIGS. 14A-14D illustrate a vehicle capable of steering autonomously to merge and diverge among various travel and access lanes in accordance with different exemplary embodiments. The vehicles 14A-14D illustrated in FIGS. 14A-14D are generally similar to each other and to vehicles 14 shown in FIGS. 1-2, except as otherwise noted. The vehicles 14A-14D in accordance with the exemplary embodiments in FIGS. 14A-14D, have a substantially or near holonomic and substantially no-scuff steering system 14AS, 14BS, 14CS, 14DS. In the embodiment shown in FIG. 14A, the vehicle steering system 14AS has four independently powered and steerable wheels 14AW to provide near holonomic movement without scuffing. The embodiment shown in FIG. 14B has independently drive wheels, (on opposite sides) of the vehicle and a free caster. The exemplary embodiment shown in FIG. 14C has two steerable wheels 14CSW at one side of the vehicle 14C, and a single centered drive wheel 14CDW at the other end of the vehicle. The exemplary embodiment in FIG. 14D has two steerable wheels 14DSW and two wheels on a differential drive axis 14DA. In alternate embodiments, the vehicle may have any other desired steering system. The autonomous steering allows the vehicles substantially free movement between travel and access lanes (TL, AL, see FIGS. 1-2) of the guideway. The location of points of furcation between travel and access lanes may be located as desired with minimal or no infrastructure impact (to facilitate tool movement, for example) or even dynamically (to avoid unexpected obstacles such as a disabled vehicles). Each vehicle may have an on board processor (not shown) with suitable memory to store a facility “map” to facilitate self-directed routing to the desired destination. If a blocked path is encountered, the vehicle may have the capability to adjust the trajectory to navigate around the obstruction along the guideway or to select an alternative path or guideway. Vehicles may also be provided with a wireless communication device (not shown) for wireless communication with other vehicles and/or base stations to enable information sharing for purposes such as dispatch coordination, location verification, error reporting, and path accessibility status. As noted before, the exemplary vehicles may traverse one or more flat, substantially featureless surfaces—ideally, the floor of the facility to minimize guideway capital investment and facilitate retrofitting to existing fabs. Such vehicles are contrasted with traditional (autonomous guided vehicles) AGVs that have been employed in semiconductor material handling. Typically, conventional AGVS load and unload payloads at operator interface points (e.g., at the 900 mm elevation in 300 mm wafer processing facilities) while navigating along the floor. To accommodate dynamic loads, conventional AGVs are tall; to prevent tip-over, particularly during seismic events, they are designed with a low center of gravity, and possess a mass much greater than that of the payload. As a consequence, robust operator integrity systems and performance limitations (such as reduced speed) are employed to allow them to properly co-exist with human operators. The vehicles 14 in this embodiment are intended to be used for point-to-point transfer only, on the floor or on dedicated guideway decks, therefore their (size and mass) scale is closer to that of the payload to be conveyed and rendering them dramatically more user friendly to operators. The small size of the vehicles allows them also to be manipulated easily by installation and/or service personnel. Referring to FIG. 14E, accommodations may be added to the vehicle 14E to assist in manual handling (e.g., for recovery_) such as features which accept a pole to allow manipulation of the vehicle without compromising ergonomics.

As noted before, in the vicinity of process tools, or, more generally, sources and destinations S, an access lane (or siding) AL is provided where vehicles may decelerate, stop, and if desired transfer carriers (FIG. 1). The vehicle 14 moves from the high-speed travel lane into the access lane and decelerates to a stop then the vehicle delivers the carrier to a process tool, a tool buffer, or a storage shelf via interface I. When the carrier transfer is complete, the vehicle 14 accelerates in the access lane AL and merges back into a travel lane TL. While in the travel lane TL, the vehicle 14 may travel at a relatively constant velocity directly to a siding ALL Ali on travel lane AL associated with the new destination. Thus, access lane AL provides sidings for the travel path TL, and conversely, the portions TLT of the travel path TL adjoining the access path AL provide a bypass to the sidings AL.

Referring now to FIGS. 3A-3C, routing may be accomplished with a binary (merge-diverge) path selection scheme, with the active switching elements 14SW, 14ST located on the vehicles 14. FIG. 3A shows an exemplary embodiment in which the vehicle has active switching elements 14SW, 14ST. In this embodiment, the vehicle has guidance or switching element 14SW at an end of the vehicle facing the travel direction T, A (one element 14SW is shown, though the vehicle may have a switching element at each end). The switching element 14SW may be mechanical or electronic. For example, the mechanical switch may include a cam surface, such as formed by a cam plate or cam rollers that is pivotably mounted to the vehicle chassis. The cam surface may be actuated or passive, and cooperates with the guidance surface S16T, S16A of the guidance system 16 in the guideway 12 (see FIG. 1) to position the cam surface in the direction of the path T1, AL1, Ali desired (see FIG. 1). The cam surface is connected by a suitable transmission mechanism or system (not shown) to steering system 14ST (e.g. steerable wheels/rollers as shown in FIGS. 14A-14D, steerable magnets in the case the vehicle is borne by a magnetic levitation system). The input from the cam surface is transmitted mechanically or electronically to the steering gear 14ST to steer movement of the vehicle on the desired path TL, AL. In the case the switching element 14SW is electronic, a suitable sensor or detector is included to sense a desired characteristics (e.g. magnetic field, optical or RF signals) from the electronic guidance means 16, and generate a steering signal processed by a servo or any other suitable steering motor controller to effect steering form the steering gear 14ST. The active switching elements 14SW, 14ST on the vehicle 14 allow the vehicle to perform the switch, rather than relying on active track elements. This eliminates a potential single point of failure that could disable a portion of the network. It also affords flexibility in accommodating distributed or centralized control with minimal communication overhead.

FIG. 3B illustrates another exemplary embodiment, wherein moveable switches 16W may be incorporated in the track, for example, to minimize the complexity of the vehicles. As seen in FIG. 3B, in this embodiment, the guidance system 16 has a switching element 16SW located at furcation 20 along travel path TL. The switching element 16SW is illustrated in this embodiment as being a mechanical element, though the switching element may also be electronic (with no moving parts). For example, the mechanical element has a switch plate or member 40 that is actuated by a suitable motor or actuator 42. The switch plate 40 is actuated by actuator 42 between a first position O, in which the switch plate directs/guides the vehicle 14 to continue on travel path TL, and a second position P in which the switch plate directs the vehicle away (or onto depending on direction) from path TL and onto access path AL. Electronic switching (not shown) may be used in the embodiments where the vehicle is supported and traverses in guideway 12 (see FIG. 1A) using contactless means such as magnetic levitation or air bearings. The electronic switch is electronically analogous to the mechanical switching 16SW shown in FIG. 3B but in place of the movable switch plate, generating for example a magnetic force operating to direct the vehicle to continue along travel path TL or move onto access path AL. A possible hybrid approach involves using the vehicle to deflect a selectively compliant track section by adhering to a cam surface as shown in FIG. 3C. In this exemplary embodiment, the guide means 16 include passively selectable switch element 16SW located at a furcation 20 merging/diverging paths TL, AL. The switch element 16SW is pivotable or movable between position O (substantially aligned with path TL) and position P (for transfer to path AL). The guide means 16 may also have a grounded cam surface 16G as shown. The vehicle 14, has a switch element 14SW, similar to the embodiment in FIG. 1, but in this embodiment the switching element 14SW on the vehicle operates to cause move of the switch 16SW on the guideway thereby effecting desired steering of the vehicle 14. The vehicle switching element here includes cam follower 14C following grounded cam surface 16G on the guideway, and actuation member 14S connected to the cam follower 14C by a suitable transmission system 14T. The actuation member 14S is positioned, based on input (mechanical or otherwise) from the cam follower 14C, and in turn acts on the movable switch element 16SW of the guideway 12 to position it in either position O or position P.

In addition to merging to and from access lanes, vehicles may switch between converging and diverging travel lanes to optimize their path from source to destination. Note that transport capacity may be increased by employing additional local, or fab-wide, vertically stacked parallel guideways 12D, 12L, as shown in FIGS. 4A-4B, and 5A-5B. Several travel “decks” 12U, 12L may be stacked and have similar or opposed desired travel directions. In the embodiments shown in FIGS. 4A-4B, 5A-5B, only two decks are shown for example purposes. Though in alternate embodiments any desired number of decks may be used. Decks 12U, 12L are each substantially similar to guideway 12 described before. Such decks may be adjacent to one another as shown, or deployed at different heights, as for example, one elevated guideway and one floor-level guideway. In the embodiment shown in FIGS. 5A-5B, a carrier transfer opening is located in the decks 12V, 12L as seen in FIG. 5B, in this embodiment, the carrier openings OP are aligned with each other. This allows a vehicle on the upper deck to transfer a carrier through the lower deck. In alternate embodiments, only the lower deck may have carrier openings.

The horizontal displacement between travel and access lanes in the exemplary embodiment described before is but one method to effect the desired separation between transport paths (where vehicles may travel between sources and destinations at a substantially constant speed) and access paths (where vehicles may accelerate/decelerate and stop—e.g., to transfer loads and/or recharge). Alternatives include merging and diverging between and among vertically displaced tracks, and allowing vehicles to pass other vehicles stopped in the same track by displacing some or all of the vehicle structure as desired.

FIGS. 9A-9E are schematic elevation views of a transport vehicle 114A-114E of the transport system provided with an integral elevator mechanism in accordance with different respective exemplary embodiments. Except as otherwise noted, the vehicles are generally similar to each other, each having carrier support 114ACS capable of supporting at least one carrier, and an elevator mechanism for raising and lowering the carrier support. In the embodiment shown in FIG. 9A, the elevator mechanism 114AE may comprise substantially rigid reel members that are wound and unwound to raise and lower the support. In the embodiment shown in FIG. 9B, the elevator mechanism 114BE may have scissoring members which are slidable at one end relative to the vehicle frame. Height adjustment is achieved by scissoring the members as desired via a motor and lead screw. In the embodiment shown in FIG. 9C, the elevator 114CE has a three or four point link system that folds up and down when powered by a motor and lead screw. In the embodiment shown in FIG. 9D, the elevator 114DE may have a telescoping rail or column arrangement, and in the embodiment shown in FIG. 9E, the elevator may have interlocking chain links capable of being wound and unwound. As may be realized, in alternate embodiment, any suitable elevating system (including fluidic and/or magnetic) may be used. Vehicles may also be provided with elevator mechanism both top and bottom as shown in FIGS. 16A-16C and 17A-17C. Referring to FIGS. 16A-16C and 17A-17C a vehicle 214 transitioning from the lower 12L to upper track 12U. The vehicle 214 in this embodiment is generally similar to vehicles 114A-114E shown in FIG. 9A-9E, except in this embodiment vehicle 214 has top and bottom elevator mechanisms as shown. As may be realized from FIGS. 16B and 17B, one mechanism is to raise half-way up from the lower wheels while the upper mechanism raises the upper wheels the remainder of the way to the upper track. In alternate embodiments, the vehicle may have a single elevator with sufficient reach. After the upper wheels are attached to the upper track the lower wheels may be retracted and result in the configuration shown in FIGS. 16C and 17C. Transition of the vehicle from top to bottom guideways would be performed in the reverse manner. In this manner, the vehicle may hop over or under impeding vehicles on either upper or lower tracks. In this exemplary embodiment, the vehicle when riding along the upper track 12U, is suspended from the upper track. The vehicle upper wheels may be held onto the upper track by any suitable means. For example, in the exemplary embodiment illustrated in FIG. 18A a vehicle 214′ is attached to the upper track by magnetic attraction. In this embodiment the upper track includes magnetic material, and the vehicle has a magnet 214M′ (permanent or electro/magnetic) or a permanent/electro-magnetic chuck, as shown in FIG. 12D, that may be activated to hold the vehicle to the upper track. The chuck has a safe mode to maintain the vehicle on the track in the event of power interruption. In alternate embodiments, the vehicle may include magnetic material attracted to a suitable magnet in the track. FIG. 18 shows a vehicle 214″ on the upper track supported by a support surface 12US under the wheels. FIG. 18 is a side view that shows vehicle 214″ transitioning from the lower to the upper track with the mechanical configuration in this exemplary embodiment. The upper support track 12US may have openings where the upper wheels could pass through after which they would engage with the upper support track, followed by the retraction of the lower wheels. To lower from the upper to lower track, the lower wheels may be lowered in contact with the lower track before an opening in the upper support track released the upper wheels.

FIGS. 19A-19C illustrate a vehicle 214″, in accordance with another exemplary embodiment, passing another vehicle 214A′″ on the same track. FIG. 19A shows vehicle 214′″ in a first running position. FIG. 19B shows vehicle 214′″ as it raises its payload. At the same time as the payload is being raised the wheels 214W′″ are moved outward in the direction of arrows X′″. This may be done by steering the wheels 214W′″ (which may be mounted on laterally displaceable linkage (not shown) as the vehicle moves forward. FIG. 19C shows vehicle 214′″ in its up position with wheels in an out position. In this condition, vehicle 214A′″ may pass under vehicle 214′″ between its wheels as shown. The opposite (i.e. inverted position) of this can be accomplished for a vehicle running on an upper track.

In alternate embodiments, transition between vertically displaced tracks if desired, may be accomplished by incorporating ramps (similar to access lanes AL shown in FIG. 1 but providing offsets from travel path TL in both horizontal and vertical directions) along with horizontal vehicle steering or horizontal switches similar to those in FIG. 3A-3C. In this case vehicles would merge to a ramp, follow the ramp to the desired elevation, then merge into the appropriate travel deck. If such vertical displacement of vehicles were desired in an access lane, a vertical track switch as depicted in FIG. 6 could be employed. In this case, the vertical displacement may be achieved by driving a vehicle 14 to an elevator 12E that moves vehicles between vertically offset lanes 12U, 12L. Such an elevator may have extra guideway decks 12E1-12E3, as depicted in FIG. 6, to replace the section used to transfer the vehicle, thus restoring a travel path for following vehicles.

As noted before, it may be desired to provide guideways 12 with default travel directions, indicated by arrows T1, A1, in FIG. 1, the vehicles 14 may have the capability of bi-directional travel to accommodate flexible routing and anomaly (e.g., obstructed path) handling. Bi-directional motion is achieved by controlling the vehicle drive motors 14M in a forward and reverse direction. If a vehicle 14 becomes disabled, the drive motors may be neutralized and the vehicle may be pushed or pulled to a suitable siding by another vehicle. The “towing” vehicle may be another standard vehicle or a dedicated recovery vehicle 14R (see FIG. 1A). In either case, the towing vehicle has the capability of overriding the switching element 14SW (see FIGS. 3A-3C) or steering (see FIGS. 14A-14D) of the disabled vehicle to force its transition to an access lane. In the exemplary embodiment, this may be accomplished with a mechanical engagement using any suitable coupling (not shown). Alternatively, other vehicles may simply avoid a disabled vehicle by selecting alternate paths to their destinations (until the disabled vehicle is recovered by an operator) and/or steering around the disabled vehicle using a local obstacle detection sensing and a collision avoidance algorithm.

Referring now to FIG. 10, there is shown a schematic elevation view of a vehicle 314 at an interface station I of guideway 12 in accordance with another exemplary embodiment. Except as otherwise noted vehicle 314 is substantially similar to vehicles 14, 114, 214 described before. In this exemplary embodiment, vehicles 314 may have the capacity to hold two or more carriers C1, C2 simultaneously. Two carriers C are shown in FIG. 10 for example purposes, though the vehicle capacity may be any desired number of carriers. In this embodiment, vehicle 314 generally transport one carrier C fewer than the maximum, capacity leaving an open position 314S1, 324S2 to enable “fast-swapping” (i.e., the introduction of one carrier immediately prior to, or simultaneously with, the extraction of another). The vehicle may interface with a handling system located at the tool station S to effect the fast swap transfer of carriers between vehicle 314 and handling system. In this embodiment, the handling system may transport the carriers to desired buffer and/or load port stations at the tool stations. The carrier 314 supports 314S1, 314S2, (as noted above two supports are shown, but the vehicle may have any desired number of carrier storage spaces) may be stacked vertically to accommodate side access or side-by-side for top access (e.g., by an overhead hoist). In either case, carriers may be supported from below (e.g., nesting on a horizontally disposed kinematic coupling) or using features on the top or sides of the carrier. For example, in the embodiment illustrated in FIG. 10, the carrier supports on the vehicle are configured to employ a side coupling which may be used alone if desired in cooperation with suitable carriers (e.g., reduced lot carriers as described before. FIG. 11 illustrates a representative support 314S′ of the vehicle 314 (see FIG. 10) coupled to a face/side of carrier C. The coupling between support 314S′ and carrier may be at the kinematic registration/coupling face of the carrier used when the carrier is registered to a tool station load port. In this embodiment, the carrier may be a face opening carrier with the registration features located on the face with the opening. In this manner a single set of registration may be provided to the carrier commonly used for all carrier docking whether to a tool station, transport vehicle, etc. In alternate embodiments, coupling between the carrier support structure on the vehicle and carrier may be to any desired face/surface of the carrier. The coupling 314SC between support structure 314S1 and carrier may be of any suitable type. For example, passive coupling or active coupling systems may be used similar to the registration systems disclosed in U.S. patent application titled “ELEVATOR-BASED TOOL LOADING AND BUFFERING SYSTEM” previously incorporated by reference. By way of example, the coupling 314SC may include a permanent electro-magnetic chuck as illustrated in FIG. 12D that interacts with magnetic material in the carrier C. FIGS. 12A-12C show a carrier CA, CB, CC having magnetic material CAM, CBM, CCM positioned at or proximate the registration face of the carrier in accordance with a number of different embodiments. The permanent electromagnetic chuck is located in the vehicle support structure 314S1 and is arranged to suit the placement of the magnetic material in the carrier. Activation of the chuck captures the carrier to the vehicle and deactivation releases the carrier vehicle coupling. In any case, as noted before the configuration of support may be common among the vehicle nests and carrier nesting locations associated with tool interface devices (buffers, loadports, and the like) to minimize overall automation hardware complexity. Such a pass-through D enables placement of the access lane directly over the loadports, thereby reducing the aisle width required to accommodate elevated guideways. The active element transitioning carriers to and from vehicles may reside on the vehicle or the mating equipment, or be grounded at the point of transfer.

In the exemplary embodiment illustrated in FIGS. 8A-8C, the vehicle drives directly to the tool loadport, eliminating a separate carrier loading mechanism for transferring carriers from vehicle to load port docking stations. In the exemplary embodiment shown, upper and lower guideways 12U, 12L are located at elevations above and below the tool loading height. The upper and lower guideway 12U, 12L and vehicles are similar to those previously described. FIG. 8A shows a section view through the aisle of the FAB in which the guideways 12U, 12L are situated with tool stations S on either side of the guideways. This arrangement is exemplary and any other suitable arrangement may be provided. A load-port is attached to the front face of the tool station at a desired elevation (e.g. above) 900 mm. The vehicles 214 are located on the guideways as shown. The guideways in this embodiment are spaced vertically apart such that the vehicles on the lower and upper guideways do not interfere with each other at any time. Similar to FIGS. 1-2, the upper and lower guideways may each have a travel or a “fast” lane similar to lane TL in FIG. 1). In this embodiment, the travel/fast lane is located down the center and vehicles 214 may run freely at high speed while sidings (similar to access lanes AL in FIG. 1) next to the load-ports are used for the vehicles 214 to “pull off”. When a vehicle 214L has “pulled off” at a load-port, FIG. 8B. The vehicle is capable of raising, or conversely lowering, the payload C as desired to be level with any of a number of port locations thereby allowing access to any desired port locations. When the payload is at the appropriate level a mechanism located at the load-port may be used to transfer the payload to or from the vehicle. In a similar fashion, a payload may be transferred to/from a vehicle on the upper track except that the payload would be lowered from the vehicle. In this embodiment, running of the vehicles may be done with the payloads normally retracted. Although only one carrier payload is shown, the vehicle may as noted before also accommodate more than one payload at a time, (e.g. one above the other). Both payload positions may move simultaneously. FIG. 8C shows a front view of an EFEM with two load-ports, each for example with three reduced capacity carrier positions. The vehicle 214L1 on the lower track 12L is shown with its payload raised to the second level. If vehicle travel is in the direction of the arrow Y it can be seen that another vehicle 214L2, 214V on the lower or upper track 12L, 12U may access the remaining load-port to either deposit or pick-up a payload. A vehicle 214V on the upper track 12U may also pull-off above the vehicle 214L1 on the lower track and wait until the lower vehicle has retracted its payload before the upper vehicle proceeds to access the ports at this location from above. As a completed payload is being removed and replaced by a vehicle, the process tool is accessing any one of the other locations as necessary.

As noted before the guideway 12 may be positioned at any desired elevation in the FAB. Such as the FAB floor (which uses minimal added infrastructure and enables easy operator access to vehicles), and the elevated right-of-way reserved in SEMI E15 for overhead transportation. Alternatively, the guideway could be placed at other convenient elevations (e.g., below the raised metal floor, or near the loadport height). The vehicles are an exemplary flexibly deployable on guideways at any or several locations. In this way additional transport network capacity and coverage may be modified to suit the needs of a particular facility.

Security of the carrier “hand-off” between the transport system and tool loading/buffering stations may be managed by a time-optimized parallel I/O scheme similar to SEMI standards E

23 and E84. Alternatively, the transportation and tool loading hardware can be treated as an integrated system, with all sensing and computation necessary to guarantee a safe transition residing locally.

Referring now to FIG. 7, if desired, carriers C may be transitioned to positions next to one or more of the access lanes AL to provide storage or buffering of the carriers at the process tools and fab wide buffering.

It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims. 

1. A substrate transport system comprising: a guideway; and at least one transport vehicle adapted for holding at least one substrate and capable of being supported from and moving along the guideway; wherein the guideway comprises at least one travel lane for the at least one vehicle and at least one access lane extending substantially along and offset from the travel lane and configured to define selectable access on and off the travel lane for the vehicle, the selectable access being arranged so that the travel lane, access lane and selectable access define a selectable substantially restrictionless path along the guideway for the vehicle to have a substantially unrestricted selectably variable transport rate along the guideway independent of impediments to the vehicle transport rate disposed along the travel lane.
 2. The system according the claim 1, wherein the at least one travel lane and the at least one access lane are arranged to allow the at least one vehicle substantially unconstrained on and off access between the travel lane and access lane.
 3. The system according the claim 1, further comprising a controller communicably connected to the guideway and the at least one vehicle, and arranged to effect selection of the transport rate.
 4. The system according to claim 1, wherein the selectable access on and off the travel lane decouples the transport rate of the at least one vehicle along the at least one access lane from a guideway transport rate of at least another transport vehicle positioned serially adjacent to, and traveling along the guideway in a common direction with the at least one vehicle.
 5. The system according to claim 4, wherein the guideway transport rate is substantially constant along the guideway, and wherein the at least one travel lane and the at least one access lane are arranged so that the at least one vehicle and the at least other transport vehicle travel along the travel lane at the substantially constant guideway transport rate.
 6. The system according to claim 1, wherein the at least one travel lane and the at least one access lane are arranged so that the at least one transport vehicle and another serially adjacent transport vehicle traveling along the at least one travel lane in a common direction and serial sequence, can change positions relative to each other to change the serial sequence.
 7. The system according to claim 6, wherein one of the at least one transport vehicle or the other transport vehicle travel along the at least one travel lane at a guideway transport rate that is substantially constant along the guideway, when the relative positions of the transport vehicles are changed to change the serial sequence.
 8. The system according to claim 1, wherein the at least one transport vehicle is capable of being stopped on the at least one access lane without affecting transport rate of an immediately adjacent transport vehicle traveling along the guideway in a common direction with the at least one vehicle.
 9. The system according to claim 1, wherein the at least one travel lane or the at least one access lane define a bypass lane relative to each other.
 10. The system according to claim 1, wherein the at least one transport vehicle has a drive arranged to effect substantially holonomic movement of the vehicle on the guideway.
 11. A substrate transport system comprising: a guideway; and transport vehicles, each of which is adapted for holding at least one substrate and capable of being supported from and moving along the guideway; wherein a section of the guideway, defining a predetermined travel direction for the transport vehicles on the guideway, comprises at least one travel lane for the transport vehicles in the predetermined travel direction and at least one access lane offset from the travel lane and extending substantially along the travel lane in the predetermined travel direction allowing the vehicles selectable access on and off the travel lane; the travel lane and access lane being arranged to enable transport vehicles serially and proximally positioned on the travel lane and having different transport rates in the predetermined direction, so that one of the transport vehicles is overtaking another, to avoid each other by accessing the access lane substantially without restriction to the transport rate of the overtaking transport vehicle.
 12. The system according the claim 11, wherein the at least one travel lane and the at least one access lane are arranged to allow the transport vehicles substantially unconstrained on and off access between the travel lane and access lane.
 13. The system according the claim 11, further comprising a controller communicably connected to the guideway and the transport vehicles, and arranged to effect selection of the transport rate.
 14. The system according to claim 11, wherein a transport rate of the at least one transport vehicle along the at least one access lane is decoupled from a guideway transport rate of at least another transport vehicle positioned serially adjacent to, and traveling along the guideway in a common direction with the at least one transport vehicle.
 15. The system according to claim 14, wherein the guideway transport rate is substantially constant along the guideway, and wherein the at least one travel lane and the at least one access lane are arranged so that the at least one transport vehicle and the at least other transport vehicle travel along the travel lane at the substantially constant guideway transport rate.
 16. The system according to claim 11, wherein the at least one travel lane and the at least one access lane are arranged so that at least one transport vehicle and another serially adjacent transport vehicle traveling along the at least one travel lane in a common direction and serial sequence, can change positions relative to each other to change the serial sequence.
 17. The system according to claim 16, wherein one of the at least one transport vehicle or the other transport vehicle travel along the at least one travel lane at a guideway transport rate that is substantially constant along the guideway, when the relative positions of the at least one transport vehicle and the other transport vehicle are changed to change the serial sequence.
 18. The system according to claim 11, wherein at least one transport vehicle is capable of being stopped on the at least one access lane without affecting transport rate of an immediately adjacent transport vehicle traveling along the guideway in a common direction with the at least one vehicle.
 19. The system according to claim 11, wherein at least one travel lane or the at least one access lane define a bypass lane relative to each other.
 20. The system according to claim 11, wherein at least one transport vehicle has a drive arranged to effect substantially holonomic movement of the vehicle on the guideway.
 21. A substrate transport system comprising: a guideway; and at least one transport vehicle adapted for holding at least one substrate and capable of being supported from and moving along the guideway at a selectably variable transport rate; wherein the guideway comprises at least one travel lane for the at least one vehicle and at least one access lane extending substantially along and offset from the travel lane allowing the vehicle selectable access on and off the travel lane so that the selectably variable transport rate of the vehicle along the guideway is selectable substantially without restriction substantially everywhere along the guideway.
 22. A substrate transport system comprising: a guideway; and at least one transport vehicle, adapted for holding at least one substrate and capable of being supported from and moving along the guideway; wherein a section of the guideway, defining a predetermined travel direction for the at least one vehicle on the guideway, comprises at least one travel lane for the at least one vehicle in the predetermined travel direction and at least one access lane extending substantially along the travel lane in the predetermined travel direction and being arranged to allow the at least one vehicle selectable access on and off the travel lane so that the at least one vehicle traveling in the predetermined travel direction along the guideway has a predetermined travel rate substantially independent of another transport vehicle positioned serially and proximally to the at least one vehicle on the travel lane. 